Windmill and wind turbine systems are generally either horizontal axis systems, where the rotating shaft is arranged in a horizontal direction, or vertical axis, where the rotating shaft is arranged in a vertical direction.
Vertical axis wind turbines rotate in the same position irrespective of wind direction, whereas horizontal axis wind turbines must be positioned to face the wind direction in order to rotate. Advantageously, vertical axis wind turbines also rotate with relatively silent movement and fit into most landscapes.
There are a variety of conventional wings or blades used with vertical axis wind turbines, including the well-known Savonius and Darrieus designs. Multiple bladed types with convex and concave shaped wings are also used. Additional blade designs have included flaps out the back of the blade. Some blades are known to bend in the middle. Other conventional blade designs are mechanically linked to always face the best angle of attack, often using elaborate mechanical devices with which they achieve the linkage.
One particular wing design is described in U.S. Pat. No. 7,980,810 to Unno. The Unno patent describes a vertical axis wind turbines having a substantially vertical rotating shaft, a plurality of substantially vertical blades fixedly secured to the shaft, each of the blades further including a front portion, a rear portion, and a pivot axis pivotally securing the rear portion to the front portion. The rear portion is operatively arranged to pivot relative the front portion. The blades additionally include bottom edges positioned on each of the front portions. Each of the bottom edges is arranged substantially equidistant from the shaft proximate a first circumference extending substantially horizontally about the shaft. The blades further include top edges positioned on each of the front portions. Each of the top edges is arranged substantially equidistant from the shaft proximate a second circumference extending substantially horizontally about the shaft. The second circumference is smaller than the first circumference
These known wing or blade designs have certain deficiencies. Most notably, such blades receive airflow on one side to cause movement in one direction but, on the other side of the turbine, the blades are moving in a direction opposite of the same airflow. In this manner, the airflow that moves the blades in one direction can in fact oppose the movement of the blades in another direction. While the known wing or blade designs may change the angle of attached, the chamber of the known wing or blade designs remains the same and is therefore inefficient.
There is a continuing need for a more efficient wing for a vertical axis wind turbine, which is camber changing with minimal mechanical complexity. Desirably, the chamber changing wing also is self-regulating in speed during an operation of the vertical wind turbine.